Heat Store

ABSTRACT

A heat accumulator for storing thermal energy may include a container with a horizontally-extending longitudinal axis, and a heat storage material in the form of a plurality of stone-like elements contained in the container. The container may include a first opening formed at a first portion of the container, and a second opening formed at a second portion of the container, the second opening being vertically offset with respect to the first opening. An average diameter of the stone-like elements arranged in the first portion of the container may be larger than an average diameter of the stone-like elements arranged in the second portion of the container.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2015/058785 filed Apr. 23, 2015, which designates the United States of America, and claims priority to DE Application No. 10 2014 208 454.7 filed May 6, 2014, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a heat store or heat accumulator for storing thermal energy.

BACKGROUND

Heat stores are thermal energy stores which store thermal energy (heat) and thus temporally decouple the generation of electrical energy from the generation or provision of the thermal energy. The thermal energy stored by means of the heat store can then be guided directly to the consumer as heat or can be used again for generating electrical energy.

One possible heat store is a bulk material store comprising stones or bricks as bulk material. In this case, the bulk material store is typically charged by means of a fluid at a temperature of approximately 600° C.

The prior art distinguishes between vertically and horizontally oriented heat stores. In particular, in contrast to a vertical heat store, a vertical temperature front is present in a horizontal heat store. During the charging or discharging of the horizontal heat store, said vertical temperature fronts are distorted on account of the natural convection which takes place in the horizontal direction, and therefore the heat store is non-uniformly charged or discharged with respect to the temperature. This limits the efficiency of horizontal heat stores.

According to the prior art, an attempt is made to hinder the natural convection by means of horizontal and/or vertical plates arranged within the horizontal heat store. A high number of plates is typically required for this purpose, however. In the case of vertically arranged plates, the pressure losses are additionally increased when charging or discharging the horizontal heat store.

SUMMARY

One embodiment provides a heat store for storing thermal energy, comprising a container with a horizontally extending longitudinal axis, wherein the container comprises a heat store material formed from a plurality of stone-like elements, wherein the container has a first opening in a first partial region and, in a second partial region, a second opening offset vertically with respect to the first opening, wherein a mean diameter of the stone-like elements arranged in the first partial region is greater than a mean diameter of the stone-like elements arranged in the second partial region.

In one embodiment, the heat store material comprises stones, bricks and/or a ceramic material.

In one embodiment, a vertical extent of the heat store perpendicular to the longitudinal axis is at most 10 m.

In one embodiment, at least one fluid-permeable distributor plate is arranged between the heat store material arranged in the first partial region and the heat store material arranged in the second partial region.

In one embodiment, the distributor plate comprises a heat-resistant steel.

In one embodiment, the distributor plate comprises a nonwoven material.

In one embodiment, the distributor plate comprises a wire grid.

In one embodiment, a first side of the container has the first opening and a second side of the container lying opposite the first side has the second opening.

In one embodiment, the heat store includes a third and a fourth opening, wherein the third opening is arranged in the first partial region and the fourth opening is arranged in the second partial region.

In one embodiment, the first side comprises the fourth opening and the second side comprises the third opening.

Another embodiment provides a method for operating a heat store as disclosed above, in which a fluid is made to flow into the container of the heat store by means of the first or second opening and is brought into thermal contact with the heat store material, wherein the heat store is discharged by making the fluid flow in through the first opening and flow out through the second opening and/or the heat store is charged by making the fluid flow in through the second opening and flow out through the first opening.

In one embodiment of the method, the heat store is discharged by additionally making the fluid flow in through the third opening and flow out through the fourth opening.

In one embodiment of the method, the heat store is charged by additionally making the fluid flow in through the fourth opening and flow out through the third opening.

BRIEF DESCRIPTION OF THE DRAWINGS

Example aspects and embodiments of the invention are discussed below with reference to the sole drawing, FIG. 1, which shows an example heat store comprising a horizontally extending distributor plate arranged between a first and a second partial region.

DETAILED DESCRIPTION

Embodiments of the invention may provide an improved horizontal heat store.

Some embodiments provide a heat store for storing thermal energy comprises a container with a horizontally extending longitudinal axis, wherein the container comprises a heat store material formed from a plurality of stone-like elements, and the container has a first opening in a first partial region and, in a second partial region, a second opening offset vertically with respect to the first opening, wherein a mean diameter of the stone-like elements arranged in the first partial region is greater than a mean diameter of the stone-like elements arranged in the second partial region.

A horizontally oriented, or a horizontal, heat store is formed by the horizontally extending longitudinal axis.

By way of example, the mean diameter of the stone-like elements is to be considered to be a diameter, averaged over the stone-like elements, of a minimum or maximum extent of the stone-like elements. This can also provide a greater mean aspect ratio of the stone-like elements arranged in the first partial region compared to the stone-like elements arranged in the second partial region. An individual aspect ratio denotes the ratio of maximum extent to minimum extent of a stone-like element. The mean aspect ratio in turn denotes an average of the individual aspect ratios.

In the first partial region of the container, the stone-like elements arranged therein have, a greater mean diameter than the stone-like elements arranged in the second partial region. In this case, the second partial region of the container, which comprises the stone-like elements with the smaller mean diameter, forms the actual partial region of the heat store for storing the thermal energy. In this case, the first partial region is provided for the horizontal, uniform distribution of an inflowing or outflowing fluid. The fluid is distributed by the enlarged stone-like elements arranged in the first partial region, which on average have a greater diameter than the stone-like elements arranged in the second partial region. Advantageously, the distribution is thereby effected with the lowest possible pressure loss. After the uniform distribution of the fluid by means of the first partial region, the fluid flows from the first partial region into the second partial region. This gives rise to an approximately vertical flow progression of the fluid, and it is therefore the case that an approximately horizontal temperature front is established within the heat store, or the container.

In other words, the disclosed heat store permits a horizontal temperature front in a horizontal heat store. The horizontal heat store consequently makes it possible to transfer the advantage of vertical heat stores—the horizontal temperature front—to horizontally oriented heat stores. Consequently, the temperature front of the horizontal heat store is not distorted during charging, discharging and/or in phases of rest by natural convection, which now takes place in a direction perpendicular to the horizontal temperature front (vertical direction). This improves the efficiency of the heat store. Temperature gradients within the heat store are reduced by the vertical offset of the first and second openings. The vertical spacing between the first opening and the base of the container is preferably smaller than the vertical spacing between the second opening and the base of the container. Furthermore, provision is made of a smaller vertical spacing between the second opening and the cover of the container compared to a vertical spacing between the first opening and the cover of the container. In other words, the first opening is arranged in the vicinity of the base of the container and the second opening is arranged in the vicinity of the cover of the container. As a result, the first and the second opening have the mutual vertical offset. The temperature of a fluid flowing in or flowing out through the first opening is expediently lower than the temperature of a fluid flowing in or flowing out through the second opening.

Some embodiments provide a method for operating a heat store, wherein a fluid is made to flow into the container of the heat store by means of the first or second opening and is brought into thermal contact with the heat store material, wherein the heat store is discharged by making the fluid flow in through the first opening and flow out through the second opening and/or the heat store is charged by making the fluid flow in through the second opening and flow out through the first opening.

For discharging, a cold fluid is made to flow into the container of the heat store by means of the first opening arranged in the first partial region, and a hot fluid is made to flow out by means of the second opening arranged in the second partial region of the container. In this respect, the first partial region is arranged in the vicinity of the base and the second partial region is arranged in the vicinity of the cover of the container. The cold fluid in this case is at a temperature which is lower than the temperature of the heat store material. The hot fluid is at a higher temperature than the heat store material. In other words, during discharging, the heat stored in the heat store, or in the heat store material, is transferred by the thermal contact from the heat store material to the fluid. A temperature of the fluid of approximately 453.15 K (180° C.) is provided when the cold fluid flows in and a temperature of the fluid of approximately 873.15 K (600° C.) is provided when the hot fluid flows out.

What is achieved by arranging the first opening in the vicinity of the base and the second opening in the vicinity of the cover is an advantageous flow progression of the fluid through the container, this progressing from the base of the container to the cover of the container during discharging of the heat store. In this case, the fluid flowing in through the first opening is distributed within the container by the first partial region in such a manner that an approximately vertical flow progression of the fluid within the second partial region is achieved. This achieves an approximately homogeneous horizontal temperature distribution, or an approximately horizontal temperature front.

During charging of the store, the fluid is made to flow in through the second opening and flow out through the first opening.

In addition, advantages of the method according to the invention which are similar and equivalent to those of the aforementioned heat store according to the invention are achieved.

According to one embodiment, the heat store material is formed from a plurality of stone-like elements. In this respect, particular preference is given to a heat store material which comprises stones, bricks and/or a ceramic material.

This is therefore advantageous since stones, bricks and/or ceramic materials have a particularly high heat capacity, and therefore a particularly efficient heat store is formed using the aforementioned heat store materials.

Preference is given to a heat store having a vertical extent perpendicular to the longitudinal axis thereof of at most 10 m.

In other words, the heat store forms a horizontal heat store. Compared to a vertical heat store, a horizontal heat store has the advantage that the geometrical extent along the longitudinal axis, which in the case of the vertical store corresponds to the height of the store, essentially is not subjected to any limitation. In addition, horizontal heat stores are technically less complex than vertical heat stores. In this context, the longitudinal axis denotes that axis of the heat store which corresponds to the direction of its greatest geometrical extent.

According to one embodiment, at least one fluid-permeable distributor plate is arranged between the heat store material arranged in the first partial region and the heat store material arranged in the second partial region.

Advantageously, the fluid which is made to flow in in the first partial region of the container is distributed approximately uniformly and horizontally in the heat store material by means of the fluid-permeable distributor plate. In this respect, the fluid is transferred from the first partial region into the second partial region via the fluid-permeable distributor plate. This further improves the horizontal temperature front within the container.

Preference is given in this respect to a distributor plate which comprises a heat-resistant steel. This expediently ensures that the distributor plate satisfies necessary thermal requirements which arise through the arrangement of the distributor plate within the container. A distributor plate which comprises a nonwoven material or mat of fibers may be advantageous.

By configuring the distributor plate as a nonwoven material or mat of fibers, the fluid is advantageously distributed approximately uniformly in the heat store material within the container. A further advantage of the nonwoven material is that the nonwoven material adapts to the shape and form of the heat store material and consequently can follow deformation of the heat store material, for example as a result of thermal loading. It is therefore not necessary for the distributor plate to have a load-bearing function. In particular, provision is made of a thin configuration of the distributor plate.

According to one embodiment, a first side of the container has the first opening and a second side of the container lying opposite the first side has the second opening.

Advantageously, the fluid thereby flows through approximately the entire heat store. This improves the efficiency of the heat store.

According to one embodiment, the heat store comprises a third and a fourth opening, wherein the third opening is arranged in the first partial region and the fourth opening is arranged in the second partial region.

In this respect, it is preferable that the third opening is arranged on the second side of the container and the fourth opening is arranged on the first side of the container. As a result, the second opening and the third opening of the container are arranged on the same side, the second side, of the container. The first and fourth openings are arranged on the first side of the container. This further improves the flow progression of the fluid within the container. In particular, the third opening is used in the manner of the first opening and the fourth opening is used in the manner of the second opening.

In other words, the heat store is charged by making the fluid flow in through the second and the fourth opening and flow out through the first and third openings. The heat store is discharged by making the fluid flow in through the first and third openings and by making the fluid flow out through the second and fourth openings.

FIG. 1 shows a heat store 1, which comprises a container 2 with a first opening 81, a second opening 82, a third opening 83 and a fourth opening 84. In this case, the first opening 81 and the fourth opening 84 are provided on a first side 91 of the container 2. The second opening 82 and the third opening 83 are arranged on a second side 92 of the container 2. The second opening 82 and the fourth opening 84 are located in the vicinity of a cover 16 of the container 2 with respect to a vertical direction V. As a result of the second and fourth openings 82, 84 being arranged in the vicinity of the cover 16, the vertical spacing between the second and fourth openings 82, 84 and the cover 16 is smaller than the vertical spacing between the second and fourth openings 82, 84 and a base 14 of the container 2. By contrast, the first and third openings 81, 83 are arranged in the vicinity of the base 14 of the container 2.The terms “horizontal” and “vertical” always refer to a gravitational force prevailing at the site of the heat store 1 (vertical direction).

The container 2 extends along a longitudinal axis, the longitudinal axis running substantially parallel to a horizontal direction H (perpendicular to the vertical direction). As a result, the heat store 1 is in the form of a horizontal heat store 1.

The single figure shows the discharging of the heat store 1 by means of the flow directions 20, 21, 22. During discharging of the heat store 1, the flow directions 20, 21, 22 illustrated are reversed. However, the advantage of the improved distribution of the fluid within the container 2 and a resultant horizontal temperature front 24 is retained during charging.

A heat store material 5 formed from a plurality of stone-like elements 4, in particular from stones 4, is arranged within a first partial region 61 of the container 2. Furthermore, a further heat store material 5 is arranged in a second partial region 62 of the container 2. In this case, the stone-like elements 4 of the heat store material 5 in the second partial region 62 have a smaller mean diameter than the stone-like elements 4 in the first partial region 61. A horizontally extending distributor plate 12 is arranged between the first partial region 61 and the second partial region 62. In this case, the distributor plate 12 serves for a further horizontal distribution of the fluid, such that an approximately horizontally extending temperature front 24 is formed.

In the illustrated case of discharging of the heat store 1, cold fluid is made to flow into the first partial region 61 of the container 2 by means of the first and third openings 81, 83. In this case, the direction in which the fluid flows in is denoted by the arrows 20 and the flow direction within the container 2 is denoted by the arrows 22.

During discharging of the heat store 1, the cold fluid flowing in by means of the first and third openings 81, 83 is at a lower temperature than the heat store material 5 arranged in the first and/or second partial region 61, 62. By virtue of the enlarged mean diameter, of the stone-like elements 4 arranged in the first partial region 61, the inflowing fluid is distributed approximately uniformly horizontally over the horizontal extent of the container 2, without excessively high pressure losses arising. Then, the fluid flows via the distributor plate 12 into the second partial region 62 of the container 2. In the process, the distributor plate 12 additionally distributes the inflowing fluid horizontally along the container 2. This results in the approximately horizontally running temperature front 24.

What is formed overall by virtue of the mutually vertically offset first and second openings 81, 82 and by virtue of the different mean diameters of the stone-like elements 4 in the first and second partial regions 61, 62 is a horizontal heat store 1, which, like a vertical heat store, has a horizontal temperature front 24. The disclosed heat store 1 therefore synergistically combines the advantages of a horizontal heat store with the advantages of a vertical heat store.

Although the invention has been described and illustrated in more detail by the preferred exemplary embodiments, the invention is not limited by the disclosed examples, or other variations can be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention. 

What is claimed is:
 1. A heat store for storing thermal energy, the heat store comprising: a container with a horizontally extending longitudinal axis, the container comprising: a heat store material comprising a plurality of stone-like elements, a first partial region of the container in which a first portion of the stone-like elements are arranged, the first partial region having a first opening, and a second partial region of the container in which a second portion of the stone-like elements are arranged, the second partial region having a second opening that is offset vertically with respect to the first opening, wherein a mean diameter of the stone-like elements arranged in the first partial region is greater than a mean diameter of the stone-like elements arranged in the second partial region.
 2. The heat store of claim 1, wherein the stone-like elements comprise at least one of stones, bricks, or a ceramic material.
 3. The heat store of claim 1, wherein a vertical extent of the heat store perpendicular to the longitudinal axis is at most 10 m.
 4. The heat store of claim 1, comprising at least one fluid-permeable distributor plate arranged between the stone-like elements arranged in the first partial region and the stone-like elements arranged in the second partial region.
 5. The heat store of claim 4, wherein the at least one distributor plate comprises a heat-resistant steel.
 6. The heat store of claim 4, wherein the at least one distributor plate comprises a nonwoven material.
 7. The heat store of claim 4, wherein the at least one distributor plate comprises a wire grid.
 8. The heat store of claim 1, wherein the first opening is located at a first side of the container and the second opening is located at a second side of the container opposite the first side.
 9. The heat store of claim 1, comprising a third opening arranged in the first partial region of the container and a fourth opening arranged in the second partial region of the container.
 10. The heat store of claim 8, wherein the first opening and the fourth opening are located at a first side of the container, and the second opening and third opening are located at a second side of the container.
 11. A method, comprising: providing a heat store including a container having a heat store material comprising a plurality of stone-like elements, with a first portion of the stone-like elements are arranged in a first partial region of the container having a first opening and a second portion of the stone-like elements arranged in a second partial region of the container having a second opening offset vertically from the first opening, wherein a mean diameter of the stone-like elements arranged in the first partial region is greater than a mean diameter of the stone-like elements arranged in the second partial region; delivering a fluid into the container of the heat store via the first opening or second opening and bringing the fluid into thermal contact with the heat store material; and at least one of: discharging the heat store by causing the fluid to flow in through the first opening and out through the second opening; or charging the heat store by causing the fluid to flow in through the second opening and flow out through the first opening.
 12. The method of claim 11, wherein: the heat store further comprises a third opening arranged in the first partial region of the container and a fourth opening arranged in the second partial region of the container, and the heat store is discharged by additionally causing the fluid to flow in through the third opening and flow out through the fourth opening.
 13. The method of claim 11, wherein: the heat store further comprises a third opening arranged in the first partial region of the container and a fourth opening arranged in the second partial region of the container, and the heat store is charged by additionally causing the fluid to flow in through the fourth opening and flow out through the third opening. 